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Noise supression

Noise supression

Noise supression

(OP)
Does anyone have any ideas on getting rid of unwanted 60 cycle noise on a 4-20ma 2 wire circuit?  thanks

RE: Noise supression

There isn't supposed to be any noise, which means that either it's not wired up correctly or it's not twisted-shielded like it's supposed to be.

Obviously, if the noise is too large, there may not be anything you can do about it short of shielding everything.


TTFN

RE: Noise supression

(OP)
The wire is shielded and grounded on one end.  The problem is intermittent, it will go for months and then start driving the plc crazy.

RE: Noise supression


If the 'loop' pair is carried in metal raceway, there may be intermittent leakage from ground to the shield part way through the run.  Isolating the cable and megging at 100 {not 1,000} volts might flush out the problem.  Also, while in operation it may be worthwhile to check for AC current in the whole cable—use a low-range clip-on ammeter around the shield and shielded pair at the grounded end.
  

RE: Noise supression

Check for other shield grounds as busbar said. If the problem persists, try grounding the shield at the other end instead(still one end only).

RE: Noise supression

Hi, its very unlikely to be pickup, especialy as its intermittent, much more likely to be a bad connection somewhere.

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